[enhancement] Non-bits-typed parametrics should be supported in procs

### What's hard to do? (limit 100 words)

Currently, the assumption that proc parametrics are bits-typed seems baked in multiple places.

### Current best alternative workaround (limit 100 words)

Use bits types everywhere- if you want to use structs, pack and unpack at proc spawn boundaries.

### Your view of the "best case XLS enhancement" (limit 100 words)

Any type should work as a proc parametric.